Why should the buyers of labor be forced to compete amongst each other but not the sellers of labor? In order to truly even the playing field, Facebook, google, apple, and the rest should unionize together to effectively negotiate with labor.

Good question. From my point of view it's because megacorps are already too powerful entities with whom individual workers have little leverage for negotiating or influencing business decisions in favor of improved working environment and socially responsible company conduct.

If FAANGS were to unionize together the field would be even more imbalanced. For instance, Apple already makes US$ 1.9 million per employee [1] which is 19x its average worker salary [2]. Nothing wrong about that, it's a profitable company, but it doesn't strike me as if they're in a unfavorable position.

[1] https://www.statista.com/statistics/217489/revenue-per-emplo...

[2] https://www.zippia.com/apple-careers-825/salary/